AS Durham double their load from 20-over to CB40 cricket today, Geoff Cook has called on his players to undergo a “big mental shift” in their ongoing pursuit of success.

The Emirates Durham ICG outfit top the County Championship and have qualified for the Friends Life t20 quarter-finals, in which they face South Group winners Hampshire Royals next month.

But this afternoon (1.05pm) sees Cook’s side return to 40-over action against Surrey Lightning, having won four and lost two of their six matches in the competition earlier in the summer.

They stand third in Group B with six to play - including Hampshire away on Tuesday, before a four-dayer at Somerset later in the week - knowing they must finish at least second to stand any chance of reaching the semis.

So Cook has asked his batsmen to turn 60-70s into hundreds, his bowlers to deliver eight overs of cheap wickets apiece, and all of his players to continue their pledge to “try to win as many games as we possibly can”.

“The 40-over game is evolving, and following a pattern of the t20 in as much as it’s a lot more aggressive,” said Cook, who revealed South African 20-over recruit David Miller will return home until the Friends Life t20 quarter-finals next month.

“It sounds an obvious thing to say, but it’s almost like two t20 matches together.

“But at the same time there is a need for batsmen to be able to concentrate for those 40 overs.

“In t20 cricket you’re looking for guys to get 60-70 runs, and if they get more that’s a real bonus. In 40-over cricket you shift back to hundreds – that’s what you’re looking for your top order to get.

“So it’s a big mental shift, and for the bowlers too.

“They have to be able to bowl eight overs at a standard where they’re going to go for wickets but look to reduce the damage as well.

“You saw on Thursday night (in a t20 win over Northamptonshire Steelbacks) that Graham Onions’ was a class opening spell (taking the first two wickets), and that’s the sort of standard that helps you survive in limited-overs cricket.

“We brought Graham back because Chris Rushworth and Mitch Claydon have had mixed fortunes in 20-over cricket.

“It’s hard work opening the bowling and bowling at the end. They’d done it for 15 games, give or take a few rained off.

“It’s been tough, and in the last couple Chris perhaps displayed a little bit of a lack of confidence, so it was a good time to bring Graham back.

“Now we have two 40-over matches before a four-day game, so again it’s about balancing the books and trying to keep players fresh.

“We have a vital four-day game coming up at Somerset and two 40-over games in three days is a hectic schedule.

“But I would like to think Graham would play in certainly at least one of the 40-over games.”

Seeking to go as far as possible in yet another format, Cook - who will recall Aussie Michael Di Venuto to the side - added: “We were starting to form a bit of a pattern in the CB40.

“Ben Stokes was central to that and unfortunately he’s out injured, so we’ll probably have to jiggle around the batting order a little bit.

“Michael Di Venuto will probably come in at the top of the order, for a couple of reasons; to try and replace Stokes and also to try and get him into a bit of form for the four-day match coming up.

“We were disappointed in the penultimate two games in the t20 that we didn’t nail a quarter-final place, but we got there with a little help from Nottinghamshire Outlaws (who beat Worcestershire Royals on Friday night).

“But with the 40-over format, we’ll just try to win as many games as we can and hopefully qualify for the next stage.”